Various anchor assemblies have been used to reinforce underground passageways, mines and the like to minimize the hazards associated therewith. Well known anchor assemblies include full column resin systems, mechanical expansion systems and combined resin-mechanical expansion systems. The present invention is particularly useful in the latter type of anchor systems, i.e. combined resin-mechanical expansion systems. However, it will be readily appreciated that the present invention may be used in solely mechanical expansion systems.
Combined resin-mechanical expansion systems generally include a two compartment cartridge consisting of a resin and a catalyst and an anchor assembly threaded on a mine roof bolt. An example of such an assembly is disclosed in U.S. Pat. No. 4,664,561 assigned to the assignee of the present invention. The anchor assembly therein includes a bearing plate resting on the head of the bolt and a mechanical expansion unit threaded onto the opposite end thereof. Conventionally, mechanical expansion units include a camming plug and an expandable shell. Further, a bail or threaded support nut is used in conjunction with the mechanical expansion unit to support the expandable shell during installation of the bolt. The two compartment cartridge is inserted into a bore hole formed in a substrate followed by the anchor assembly threaded on a bolt. Once the resin cartridge is punctured by the insertion of the anchor assembly a sufficient distance in the bore hole, the resin and the catalyst flow downwardly about the components of the anchor assembly to surround the same.
The mechanical expansion unit is activated by rotating the bolt relative to the expansion shell and the camming plug to draw the camming plug downwardly thereby forcing the fingers of the expandable shell into engagement with the sidewalls of the bore hole. In this manner, the bolt is mechanically secured to the substrate. The bolt is further supported in the bore hole of the substrate by the resin when hardened.
After the shell has been fully expanded, further rotation of the bolt causes the camming plug to be drawn down into the expansion shell and thereby create tension in the bolt shank. This forces the bearing plate against the roof of the substrate to compresses the competent strata into a beam. This procedure significantly improves the load bearing characteristics of the roof of the substrate.
Conventional mine roof bolts have a diameter of at least 5/8". Also, it has been known to provide an expandable shell having 11/4 outside diameter for use with the previously identified mine-roof bolts. When members of these dimensions are employed, it is customary to bore a hole in the competent strata slightly larger than 11/4". However, it has been found desirable to form smaller bore holes, for example, slightly greater than 1" as is explained in U.S. Pat. No. 4,913,513. In these instances, a conventional 5/8" bolt is still used. However, to permit insertion of the anchor assembly into the bore hole, it is necessary to reduce the size of the expandable shell. More specifically, an expandable shell having approximately 1" outer diameter is employed. It has been found, when installing mine roof bolts in the smaller bore holes using the scaled down expandable shells, that the flow of the resin and catalyst downwardly from the upper surface of the camming plug is sometimes inhibited. Restricted flow of the resin and catalyst may preclude the resin from flowing evenly about the camming plug and the expandable shell as well as the other components of the anchor assembly and the bolt to secure the same to the inside walls of the bore hole. Accordingly, the bonding effect of the resin may be minimized.